Marshall Bass Amp with Dry Joint

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raynor
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Marshall Bass Amp with Dry Joint

Post by raynor » Mon Nov 05, 2007 7:16 pm

I have a Marshall B150 Bass Amp which developed a dry joint. The breakdown of sound is audio and not power. The amp dies at times and I give it a whack on top and it springs back to life only to cut out again at a later stage. I openend the amp but failed to find the fault.I sent it away for repair to a "Specilist Marshall" repairman who gave me a quote of $300. I found this amount to be excessive so did not have it repaired. My question is : Am I being ripped off or what? The amp has only 1 valve which I did replace .

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timi
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Re: Bass Amp

Post by timi » Mon Nov 05, 2007 11:57 pm

That seems like a lot for some dry solders and one 12ax7.

I had an amp with similar problems once, the repair was $45 from Weta in Wellington. I didn't need a preamp tube though, but they only cost $30.

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Jazzbass
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Re: Bass Amp

Post by Jazzbass » Tue Nov 06, 2007 1:17 pm

I have had similar problems - also with Marshall amps - which is why I no longer have them.

Here's how I fix them:

remove the amp
place amp on bench or on top of combo if easier
power up
wait for fault to show itself
tap components with a ball-point pen or other similar plastic rod
wobble components
This nearly always isolates the problem area
Turn power off
re-solder all joints around component fault area
re-test

If you still can't find it, basically just turn everything off and resolder EVERY joint. It doesn't take long and it WILL fix it, if the problem is a dry joint.

$300 is a rip-off! That's more than the amp's worth.

miked
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Re: Bass Amp

Post by miked » Tue Feb 12, 2008 4:48 pm

Hi raynor, did you fix your fault?
I have a Marshall 7400 head which developed a similar problem (I think the B150 is based on the 7200/7400).
Solution: The effects send/return jacks go high resistance if not in use so I just plug a looping link into them, never had a problem since. :D

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timi
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Re: Bass Amp

Post by timi » Tue Feb 12, 2008 8:15 pm

Dodgy fx loops are also a common problem (the jacks are TRS for switching the loop on when a jack is inserted). Running a short patch cable in the fx loop can somestimes be a temporary fix.

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